(a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device including a gate electrode to which cobalt silicide is applied.
(b) Discussion of the Related Art
The performance of a transistor in a semiconductor device is related to a combination of speed, driving current, leakage current, etc. Thus, to enhance the transistor performance by increasing speed while decreasing leakage current, attempts have been made to reduce resistance of source and drain regions or a gate electrode.
A known method used to reduce the resistance of these regions is to form a metal silicide layer overlying surfaces of source and drain regions or an upper surface of a gate electrode. Cobalt silicide is used as the metal silicide, as cobalt silicide provides favorable leakage current and resistance properties.
In a known gate electrode formation process, cobalt is deposited on a silicon wafer having a predetermined gate electrode and source and drain electrodes. A cobalt film is formed on surfaces of the source and drain electrodes and an upper surface of the gate electrode. Then, a protection metal film is formed on the cobalt film using titanium (Ti) or titanium nitride (TiN), etc. Next, a thermal treatment is performed to form a cobalt silicide film by a reaction of cobalt and silicon. The protection metal film is to prevent a surface of the cobalt film from being nitrified, the cobalt from being silicified too quickly, or the cobalt silicide film from being formed with too great a thickness.
However, when the protection metal film is erroneously or abnormally formed relatively thin as compared to a predetermined thickness, the cobalt silicide film is formed too thick on a portion of the surface of the gate electrode or a portion of the surfaces of the source and drain regions. In such a case, a moat resistance and a resistance of poly-silicide decrease, and an RC delay constant falls outside of a predetermined condition, such that the semiconductor device does not function optimally. Further, the diode leakage current increases, so that operation of the device may be precluded. Thus, the wafer is disposed of when the protection metal film has a thickness less than the predetermined thickness.